Process for the preparation of stable mixtures of bitumen and polymer

Abstract

Mixtures of bitumen and thermoplastic polymer stable to storage are prepared by a process comprising: (i) mixing a bituminous product having a content of total asphaltenes, resins, saturated and aromatic products which satisfies the condition that the I c value is between 0.200 and 0.270 in the expression: I.sub.c =(C7+C5+S)/(A+R) with a thermoplastic polymer, the reaction being carried out at a temperature of between 160° C. and 200° C. and for a time of between 15 and 120 minutes and (ii) diluting the bituminous composition obtained in (i) with a bitumen or bituminous component having an I c defined as specified above in (i) of between 0.270 and 0.700 in such a quantity that the final concentration of the polymer is between 2.5 and 15% by weight, and heating to a temperature of between 160° C. and 200° C. for a time of between 30 and 90 minutes.

We claim: 
     
       1. Process for the preparation of mixtures of bitumen and thermoplastic polymer stable to storage characterized in that: (i) a bituminous product having a content of total asphaltenes, resins, saturated and aromatic products which satisfies the condition that the I c  value is between 0.200 and 0.270 in the expression:   I.sub.c =(C7+C5+S)/(A+R)     wherein     C7=concentration of asphaltenes precipitated with N-heptane in % weight,   C5=concentration of asphaltenes precipitated with N-pentane in % weight;   S=concentration of saturated products (parafins) in % weight;   A=concentration of aromatics in % weight; and   R=concentration of resins in % weight is reacted at a temperature of between 160° C. and 200° C. and for a time of between 15 and 120 minutes with a thermoplastic polymer, selected from the group consisting of copolymers and elastomers and elastomeric copolymers, in a weight ratio between each other of between 80:20 and 95:5; and (ii) the resulting bituminous composition is diluted with a bitumen or a bituminous component having an I c  defined as specified in (i) of between 0.270 and 0.700 in such a quantity that the final concentration of the polymer is between 2.5 and 15%, and this is heated to a temperature of between 160° C. and 200° C. for a time of between 30 and 90 minutes.     
     
     
       2. Process according to claim 1, characterized in that in step (i) the bituminous product consists of one or more components selected from aromatic distillates of petroleum or distillation bitumens. 
     
     
       3. Process according to claim 2, characterized in that the bituminous product consists of an aromatic extract from a lubricant base and a vacuum residue in a weight ratio between each other that is such that the resulting mixture has an I c  of between 0.200 and 0.270. 
     
     
       4. Process according to claim 1, characterized in that the bituminous product in step (i) has an I c  of between 0.240 and 0.260. 
     
     
       5. Process according to claim 1, characterized in that in step (ii) the bitumen and bituminous component are selected from a distillation bitumen, a precipitation bitumen, a oxidated bitumen or a bitumen obtained by mixing various components of a petroleum origin. 
     
     
       6. Process according to claim 5, characterized in that the bitumen is selected from the group consisting of a bitumen from propane, a bitumen from visbreaking, a bitumen from a vacuum process, and a bitumen reconstructed with lube cycle components. 
     
     
       7. Process according to claim 1, characterized in that in step (ii) the bitumen and bituminous component have an I c  of between 0.280 and 0.500. 
     
     
       8. Process according to claim 1, characterized in that the polymer is a block copolymer containing vinyl benzenes and conjugated dienes having a radial structure which can be represented with the formula X(A-B) m , wherein A represents a block obtained from vinylaromatic monomers, B is a block obtained from dienic monomers, X is a radical deriving from a coupling agent and m is a number from 3 to 5. 
     
     
       9. Process according to claim 8, characterized in that the copolymer contains polystyrene and polybutadiene blocks with a ratio styrene/butadiene of between 20/80 and 40/60 and a weight average molecular weight of between 50,000 and 1,000,000. 
     
     
       10. Process according to claim 8, characterized in that the radial copolymer has a ratio styrene/butadiene of between 25/75 and 35/65 and a weight average molecular weight of between 100,000 and 400,000. 
     
     
       11. Process according to claim 8, characterized in that the copolymer is in an oil-extended form. 
     
     
       12. Process according to claim 1, characterized in that the temperature in steps (i) and (ii) is between 175° C. and 185° C. and the reaction time in the single steps is between 30 and 60 minutes. 
     
     
       13. Process according to claim 1, characterized in that in step (i) the weight ratio between the bituminous product and the polymer is between 85:15 and 95:5. 
     
     
       14. Process according to claim 1, characterized in that in step (ii) the weight ratio between the bituminous product and the polymer is between 98:2 and 94:6. 
     
     
       15. Mixtures of bitumen and polymer stable to storage prepared by the process according to the claim 14.